Fix stepping over await statements

runtime/vm/debugger.cc

Index: runtime/vm/debugger.cc
diff --git a/runtime/vm/debugger.cc b/runtime/vm/debugger.cc
index a4afc16275873e52c3b3dac54563a4b5253b7e86..c076689dac5508438ec321fad19b6df5dc83e06b 100644
--- a/runtime/vm/debugger.cc
+++ b/runtime/vm/debugger.cc
@@ -376,6 +376,17 @@ Breakpoint* BreakpointLocation::AddPerClosure(Debugger* dbg,
     if (bpt->IsPerClosure() && bpt->closure() == closure.raw()) break;
     bpt = bpt->next();
   }
+  if (for_over_await &&
+      (bpt != NULL) &&
+      (bpt == dbg->synthetic_async_breakpoint_)) {
+    // If the debugger is paused after stepping over an await statement,

[Cutch, 2016/09/21 23:43:45]

I wonder if we could just do the following in this block:

if (for_over_await ....) {
  RemoveBreakpoint(bpt->id());
  remove_synthetic_async_breakpoint = false;   /* this controls whether or not
synthetic_async_breakpoint gets removed after the stepping */
  bpt = NULL;
}

...

This way we still create a new synthetic breakpoint.

[hausner, 2016/09/21 23:59:28]

Why is it important to create a new synthetic BP each time? Also, I think 
synthetic_async_breakpoint_ should be set to NULL if the breakpoint is refers to
is deleted.

+    // the synthetic breakpoint is temporarily kept in
+    // synthetic_async_breakpoint_ so it can be deleted when the step
+    // command resumes.
+    // If another step request over an async statement is issued, make
+    // sure the synthetic breakpoint does not get deleted.
+    dbg->synthetic_async_breakpoint_ = NULL;
+  }
   if (bpt == NULL) {
     bpt = new Breakpoint(dbg->nextId(), this);
     bpt->SetIsPerClosure(closure);